linux-kernel - Re: [RFC,PATCH 1/3] Add a common struct clk

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Date:	Thu, 10 Feb 2011 20:45:43 +0800
From:	Richard Zhao <linuxzsc@...il.com>
To:	Ryan Mallon <ryan@...ewatersys.com>
Cc:	Richard Zhao <richard.zhao@...escale.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Dima Zavin <dmitriyz@...gle.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org, Paul Mundt <lethal@...ux-sh.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Russell King <linux@....linux.org.uk>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk

On Thu, Feb 10, 2011 at 11:10:52PM +1300, Ryan Mallon wrote:
> On 10/02/11 23:03, Richard Zhao wrote:
> >On Thu, Feb 10, 2011 at 09:21:14AM +1300, Ryan Mallon wrote:
> >>On 02/09/2011 07:41 PM, Jeremy Kerr wrote:
> >>
> >>Hi Jeremy,
> >>
> >>Couple more comments below.
> >>
> >>~Ryan
> >>
> >[...]
> >>>+int clk_enable(struct clk *clk)
> >>>+{
> >>>+     unsigned long flags;
> >>>+     int ret = 0;
> >>>+
> >>>+     spin_lock_irqsave(&clk->enable_lock, flags);
> >>         WARN_ON(clk->prepare_count == 0); ?
> >>
> >>>+     if (clk->enable_count == 0&&  clk->ops->enable)
> >>>+             ret = clk->ops->enable(clk);
> >>Does it make sense to have a clock with no enable function which still
> >>returns success from clk_enable? Do we have any platforms which have
> >>NULL clk_enable functions?
> >>
> >>I think that for enable/disable at least we should require platforms to
> >>provide functions and oops if they have failed to do so. In the rare
> >>case that a platform doesn't need to do anything for enable/disable they
> >>can just supply empty functions.
> >It's possible to be NULL. So are set_rate/get_rate.
> >Ideally, if it's NULL:
> >prepare/unprepare: only call parent's prepare/unprepare
> >enable/disable: only call parent's enable/disable
> 
> No, the whole point of the generic framework is that _all_ clock
> users must call prepare/enable and disable/unprepare. Drivers, etc
> should not rely on underlying knowledge of a platform. This is why,
> for instance, clk_enable will warn if prepare count is zero.
> 
> However, I can see that a clock may be fully enabled by its prepare
> function and so the enable function is a no-op. User must still call
> both prepare and enable though. Perhaps this is what you meant?
I mean prepare/unprepare, enable/disable and get_rate ops null can be handled
in the common clock code. But it needs parent clock pointer.

Thanks
Richard
> 
> ~Ryan
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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